2.1.1 Microscopes

Question 1

resolution definition

Answer 1

the degree to which it is possible to distinguish two objects, which are very close together

Question 2

magnification definition

Answer 2

how many times bigger the image of a specimen observed is, compared to the actual size of the specimen

Question 3

magnification equation

Answer 3

magnification=size of image/size of actual

Question 4

method for using light microscope: 9 steps

Answer 4

1. Prepare sample using a glass slide, coverslip and stain
2. Plug microscope into plug socket and turn on
3. Turn light on
4. Put sample on the stage, secure with clips
5. Adjust to lowest magnification
6. Move stage all the way up
7. Use the coarse focus wheel to get sample into focus (larger field of view)
8. Move to next objective lens (use fine focus wheel to show detail)
9. Repeat with next objective lens

Question 5

light microscope: how does it work?

Answer 5

it works by passing light through a specimen and focusing the light on an eyepiece or camera, which magnifies the image.

Question 6

light microscope: what is it used for?

Answer 6

-schools and colleges
-hospitals
-universities

Question 7

light microscope: preparation of specimen

Answer 7

place a slide with cover slip and with a stain

Question 8

light microscope: maximum magnification

Answer 8

x1500

Question 9

light microscope: 2D or 3D, colour or black and white

Answer 9

2D, colour

Question 10

light microscope: resolution

Answer 10

0.2 μm

Question 11

light microscope: advantages 4

Answer 11

-relatively cheap
-easy to use
-portable
-able to study whole living specimen

Question 12

light microscope: disadvantage 1

Answer 12

-resolution is limited (as cannot increase magnification any higher with detail)

Question 13

confocal laser scanning microscope: how does it work?

Answer 13

a thick section of tissue or small living organisms are scanned with a laser beam
the laser beam is reflected by the fluorescent dyes
multiple depths of the tissue section/organisms are scanned to produce an image
(think of it like the laser beam is building up the image layer by layer)

Question 14

confocal laser scanning microscope: what is it used for?

Answer 14

-medical professions
-branches of biological research

Question 15

confocal laser scanning microscope: preparation of specimen

Answer 15

the cells being viewed must be stained with fluorescent dyes

Question 16

confocal laser scanning microscope: max magnification

Answer 16

not needed

Question 17

confocal laser scanning microscope: 2D or 3D, colour or black and white

Answer 17

3D, colour

Question 18

confocal laser scanning microscope: resolution

Answer 18

do not need

Question 19

confocal laser scanning microscope: advantages 4

Answer 19

-they can be used on thick or 3-D specimens
-they allow the external, 3-D structure of specimens to be observed
-very clear images are produced, the high resolution is due to the fact that the laser beam can be focused at a very specific depth

Question 20

confocal laser scanning microscope: disadvantages 2

Answer 20

-it is a slow process and takes a long time to obtain an image
-the laser has the potential to cause photodamage to the cells

Question 21

transmission electron microscope (TEM): how does it work?

Answer 21

use electromagnets to focus a beam of electrons, this beam of electrons is transmitted through the specimen
denser parts of the specimen absorb more electrons tf denser parts appear darker on the final image produced (produces contrast between different parts of the object being observed)

Question 22

transmission electron microscope (TEM): what is it used for?

Answer 22

-biological research

Question 23

transmission electron microscope: preparation of specimen

Answer 23

the specimen have to be chemically fixed by being dehydrated and stained with metal salts, stained in order to absorb the electrons (heavy metal compounds are often used)

Question 24

transmission electron microscope (TEM): max magnification

Answer 24

up to x 2 million

Question 25

transmission electron microscope (TEM): 2D or 3D, colour or black and white

Answer 25

2D, black and white

Question 26

transmission electron microscope (TEM): advantages 2

Answer 26

-high resolution -this allows the internal structures within cells (or even within organelles) to be seen

Question 27

transmission electron microscope (TEM): disadvantages 6

Answer 27

-specimen cannot be alive (as there is a vacuum inside of TEM, all water must be removed from specimen) -large -very expensive -need a great deal of skills and training to use -they can only be used with very thin specimens or thin sections of the object being observed -the lengthy treatment required to prepare specimens means that artefacts can be introduced (artefacts look like real structures but are actually the results of preserving and staining)

Question 28

scanning electron microscope (SEM): how does it work?

Answer 28

SEMs scan a beam of electrons across the specimen This beam bounces off the surface of the specimen and the electrons are detected, forming an image Tf SEMs can produce three-dimensional images that show the surface of specimens

Question 29

scanning election microscope (SEM): what are they used for?

Answer 29

biological research

Question 30

scanning electron microscope (SEM): preparation of specimen

Answer 30

specimen has to be placed in a vacuum and often coated with a fine film of metal

Question 31

scanning electron microscope (SEM): max magnification

Answer 31

up to 200,000x

Question 32

scanning electron microscope (SEM): 2D or 3D, colour or black and white

Answer 32

3D, black and white (the computer programme can add false colour

Question 33

what type of instruments are microscopes?

Answer 33

optical

Question 34

what scale is used for microscopes?

Answer 34

logarithmic

Question 35

what does logarithmic mean?

Answer 35

it goes up in steps, where each is 10-fold increase

Question 36

what is the effect of increasing magnification,on resolution?

Answer 36

increasing magnification, doesn’t increase resolution

Question 37

why does light limit resolution in light microscopes?

Answer 37

it is impossible to resolve two objects that are closer than half the wavelength of light (the wavelength of visible light is between 0.5 or 0.65),

Question 38

what can a light microscope observe?

Answer 38

eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts

Question 39

scanning electron microscopes (SEMs): 2 advatages

Answer 39

-they can be used on thick or 3-D specimens -they allow the external, 3-D structure of specimens to be observed

Question 40

scanning electron microscopes (SEMs): 3 disadvantages

Answer 40

-they give lower resolution images than TEMs -they cannot be used to observe live specimens -they do not produce a colour image

Question 41

what should be used to calibrate a microscope?

Answer 41

a stage micrometer